Study on Limit Loads for Safe End of Nuclear Pressure Vessel with Local Wall Thinning

Dissimilar metal welded joints are used in primary water systems of pressurized water reactor in nuclear power plant. They are mainly used to connect the ferritic steel pipe-nozzles of the pressure vessels such as reactor pressure vessels, steam generators and pressurizers with the austenitic stainless steel safe end. Thus, maintaining integrity of such joints is critical to ensure their safe service. As local wall thinning may probably appear at safe end to due to erosion and corrosion, assessment methods with local wall thinning are urgently needed. In this paper, three-dimensional finite element analysis models with and without considering local wall thinning were built for dissimilar metal welded joints connected the safe end to pipe-nozzle of the reactor pressure vessel. A detailed analysis has been carried out to the limit load research of this structure. Results show that the bending load is the main factor influencing the stress distribution change and limit load. According to finite element results, the depth of local wall thinning should be the most important factor influencing limit load solution, while circumferential local wall thinning shows very small variation. Based on the finite element results prediction equations of limit loads for safe end with local wall thinning have been proposed.